Environment definitions in task files should have precedence over predefined environment variables

docs/docs/usage.md

@@ -119,6 +119,10 @@ tasks:
 
 ### Task
 
+:::info
+Custom environment variables will **overwrite** any predefined environment variables from your shell.
+:::info
+
 You can use `env` to set custom environment variables for a specific task:
 
 ```yaml

internal/env/env.go

@@ -20,10 +20,6 @@ func Get(t *taskfile.Task) []string {
 			continue
 		}
 
-		if _, alreadySet := os.LookupEnv(k); alreadySet {
-			continue
-		}
-
 		environ = append(environ, fmt.Sprintf("%s=%s", k, str))
 	}
 

task_test.go

@@ -6,13 +6,15 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
 	"testing"
 
 	"github.com/Masterminds/semver/v3"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/go-task/task/v3"
 	"github.com/go-task/task/v3/internal/filepathext"
@@ -1832,3 +1834,29 @@ func TestBashShellOptsCommandLevel(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, "globstar\ton\n", buff.String())
 }
+
+func TestOverwriteEnvironment(t *testing.T) {
+	binary := buildTask(t)
+
+	cmd := exec.Command(binary)
+	cmd.Dir = "testdata/env_override"
+	cmd.Env = []string{"PREDEFINED=initial"}
+	require.NoError(t, cmd.Run())
+
+	output, err := os.ReadFile("testdata/env_override/output.txt")
+	require.NoError(t, err)
+	require.Equal(t, "PREDEFINED='overwritten'", string(output))
+}
+
+func buildTask(t *testing.T) string {
+	temp := t.TempDir()
+
+	binary := filepath.Join(temp, "task")
+	command := exec.Command("go", "build", "-o", binary, "cmd/task/task.go")
+	var output bytes.Buffer
+	command.Stdout = &output
+	command.Stderr = &output
+	require.NoError(t, command.Run(), &output)
+
+	return binary
+}

testdata/env_override/.gitignore

@@ -0,0 +1 @@
+*.txt

testdata/env_override/Taskfile.yaml

@@ -0,0 +1,10 @@
+version: '3'
+
+silent: true
+
+tasks:
+  default:
+    env:
+      PREDEFINED: 'overwritten'
+    cmds:
+      - echo -n "PREDEFINED='$PREDEFINED'" > output.txt